The present invention relates to film cassettes in general, and more particularly to film cassettes for x-ray films. Still more particularly, the present invention relates to film cassettes which include two cassette parts which are connected with one another by a hinge, and which respectively carry a confining plate having an area substantially corresponding to that of a film to be accommodated between the cassette parts and exerting magnetic forces over its area, and a ferromagnetic confining foil located oppositely to and magnetically attracted by the magnetic plate, wherein the x-ray film and a pair of intensifying shields are confined between the confining plate and the confining foil in the closed position of the cassette.
A cassette of this construction is known, for instance, from German patent DE-PS No. 1,112,887. This conventional cassette incorporates a sheet of an elastic material which exerts magnetic attraction forces over its entire area and which cooperates with an iron foil which is supported on the bottom of the cassette. Experience with this conventional cassette has shown that it is disadvantageous in several respects. One of the main disadvantages of this conventional cassette is that the very thin ferromagnetic foil, which simultaneously serves as a medium through which x-rays enter the internal space of the cassette, and which has a thermal expansion coefficient differing from that of the components on which this foil is supported (the difference amounting up to the factor of 10), very often becomes detached from its support and forms folds, especially when the cassette is subjected to certain temperature variations. Such temperature variations usually do not occur in a laboratory where the temperature is usually maintained at approximately the same level. However, temperature variations sufficient to have the aforementioned detrimental consequences may occur when the cassette is transferred from a well-heated treating room to an unheated storage area. Moreover, it has been established that this detachment of, and formation of folds, wrinkles or creases on, the foil occur in particular during transportation of the cassettes from one location to another in railway cars or on airplanes, especially when this transportation takes place during the wintertime or during other periods of cold weather conditions.